Self-exciting type high voltage generating apparatus utilizing piezolectric voltage transforming elements

ABSTRACT

In a self-exciting type high voltage generating apparatus utilizing a piezolectric voltage transforming element driven by an oscillator, a capacitive feedback circuit is provided between the output of the piezolectric voltage transforming element and the oscillator to lock the oscillation frequency of the oscillator to the resonance frequency of the piezolectric voltage transforming element.

United States Patent Keizi [15] 3,679,918 [4 1 July 25, 1972 [54] SELF-EXCITING TYPE HIGH VOLTAGE GENERATING APPARATUS UTILIZING PIEZOLECTRICVOLTAGE TRANSFORMING ELEMENTS [72] Inventor:

[73] Assignee:

Inoue Keizi, Yokohama, Japan Denki Onkyo Company Limited, Tokyo, Japan[22] Filed: June 19, 1970 [21] Appl.No.: 47,759

[30] Foreign Application Priority Data Dec. 30, 1969 Japan ..44/105474[52] US. Cl ..310/8.1, 310/82, 310/98, 331/163 [51] Int. Cl. ..H01v 7/00[58] Field ofSearch ..310/8.1, 8.2, 9.8, 9.7, 8.9,

POSITIVE 4 SOURCE 5 [56] References Cited UNITED STATES PATENTS1,864,368 6/1932 Nicalson ..331/163 X 3,562,792 2/1971 Berlincourt eta1. 10/81 3,516,645 6/1970 Arndt 1 ..310/8.1 2,975,354 3/1961 Rosen10/81 UN 3,421,109 1/1969 Wiggins et a1. .331/116 3,256,498 6/1966Hurtig 331/155 X 2,594,841 4/1952 Arndt ....310/8.1 X 2,859,346 11/1958Firestone et a1, ..3 10/81 X Primary Examiner-J. V. Truhe AssistantExaminerB. A. Reynolds Attorney-Chittick, Pfund, Birch, Samuels &Gauthier 1 57] ABSTRACT In a self-exciting type high voltage generatingapparatus utilizing a piezolectric voltage transforming element drivenby an oscillator, a capacitive feedback circuit is provided between theoutput of the piezolectric voltage transforming element and theoscillator to lock the oscillation frequency of the oscillator to theresonance frequency of the piezolectric voltage transforming element.

4 Claims, 3 Drawing Figures P A TENTEU Jill 25 I973 3. 6 79 9 1 8 FIG. 2

n4 l5 l2 & k 2 BLOCKING OUT PUT & HIGH VOLTAGE osc CKT RECT CKT v 3 :36I3 SYNCHRONIZING 5 CKT l m, SOURCE 5 ATTORNEY BACKGROUND OF THEINVENTION This invention relates to a novel self-exciting type highvoltage generating apparatus utilizing a piezoelectric voltagetransforming element and having a unique synchronizing system.

As shown in FIG. 1 of the accompanying drawing, a high voltagegenerating apparatus utilizing a piezoelectric voltage transformingelement generally comprises a piezoelectric voltage transforming element1 provided with two drive electrodes 2 and 3 and an output electrode 4.The drive electrode 2 is connected to one terminal of a source ofalternating current while the other drive electrode 3 is grounded. Theoutput electrode 4 is connected to a high voltage rectifier circuit 12which acts to multiply the output voltage by a factor of four andcomprised by four diodes 6, 7, 8 and 9 and capacitors l and II. A load13 is connected to the output terminal of the high voltage rectifyingcircuit 12.

When an AC voltage of a predetermined frequency is applied across driveelectrodes 2 and 3 of the piezoelectric voltage transforming elementfrom an AC source the piezoelectric voltage transforming element willresonate to produce at the output electrode 4 a high AC voltage which isabout 200 to 300 times higher than the input voltage applied acrossdrive electrodes 2 and 3. This high voltage is further stepped up andrectified by the high voltage rectifying circuit 12 to obtain a high DCvoltage which is applied to load 13.

When compared with a conventional high voltage generating apparatusutilizing a step-up transformer the high voltage generating apparatusutilizing a piezoelectric voltage transforming element as describedhereinabove enables one to use smaller circuit elements thus resultingin the miniaturization and decrease in the weight of the apparatusHowever, a conventional piezoelectric voltage transforming element ischaracterized by its ability of responding to a single frequency andlimited frequencies close thereto. Consequently, when such an element isutilized as a high voltage generating apparatus it is necessary to payspecial care to the construction of the AC source or the oscillatorvSUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a novel synchronizing system for a self-excited type highvoltage generating apparatus utilizing a piezoelectric voltagetransforming element which can stabilize the oscillation frequency ofthe oscillator.

According to this invention, there is provided a self-exciting type highvoltage generating apparatus comprising an oscillator, a piezoelectricvoltage transforming element provided with a drive electrode and anoutput electrode, means for coupling the output from the oscillator tothe drive electrode, and a capacitive feedback circuit for feeding theoutput appearing at the output electrode back to the oscillator wherebyto lock the oscillation frequency of the oscillator to the resonancefrequency of the piezoelectric voltage transforming element. Thecapacitive feedback circuit may be constituted by a capacitor of smallcapacitance and in some case may be comprised by the stray capacitanceof the apparatus.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understoodand the various objects and advantages will be more fully appreciatedfrom the following description taken in conjunction with theaccompanying drawing in which:

FIG. I shows an electrical connection to explain the principle ofoperation of a high voltage generating apparatus utilizing apiezoelectric voltage transforming element;

FIG. 2 is a block diagram to explain the principle of a synchronizingsystem of a self-exciting type high voltage generating apparatusutilizing a piezoelectric voltage transforming element and embodyingthis invention and FIG. 3 shown a detailed connection diagram oftheembodiment shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 2 of theaccompanying drawing which shows the principle of the novelsynchronizing system of a self-exciting type high voltage generatingapparatus utilizing a piezoelectric voltage transforming element and inwhich corresponding elements are designated by the same referencenumerals as in FIG. I, there is provided an oscillator 14 comprising ablocking oscillator, a nonstable multivibrator or the like. The outputof the oscillator 14 is coupled to a horizontal deflection circuit 15 ofa television receiver, for example, and the output of the circuit 15 isimpressed across a pair of drive electrodes 2 and 3 of a piezoelectricvoltage transforming element l. A portion of the output from the outputelectrode 4 of the piezoelectric voltage transforming element issupplied to a synchronizing circuit 16 in accordance with this inventionand the output from the synchronizing circuit is fed back to theoscillator 4.

In operation, the oscillation frequency of the oscillator 14 is set tobe slightly lower than the resonance frequency of the piezoelectricvoltage transforming element. The synchronizing circuit is usuallycomprised by a capacitor of small capacitance.

As the piezoelectric voltage transforming element 1 is driven byoscillator 14 through output circuit 15, a high AC voltage of aninherent oscillation frequency of the element will be induced at theoutput terminal 4 thereof. After being stepped up and rectified by thehigh voltage rectifying circuit 12, this voltage is supplied to load 13.A portion of the AC voltage appearing at the output electrode 4 of thepiezoelectric voltage transforming element is fed back to the oscillator14 through the synchronizing circuit 16 to forcibly synchronize theoscillation frequency of the oscillator with the resonance frequency ofthe piezoelectric voltage transforming element 1.

FIG. 3 shows the detail of the circuit construction of the block diagramshown in FIG. 2. In FIG. 3, the oscillator 14 is shown as a blockingoscillator comprising an NPN-type transistor 17, a transformer 21 havinga primary winding I8, a secondary winding 19 and a tertiary winding 20,resistors 22, 23 and 24 and capacitors 25 and 26. One end of a capacitor16 that comprises the synchronizing circuit is connected to the baseelectrode of transistor 17.

The output circuit 15 comprises a NPN-type transistor 29 To the baseelectrode thereof is applied the signal taken from the tertiary winding20 of the transformer 21 in the oscillator 14 through a resistor 27 anda capacitor 28 which are connected in parallel. The emitter electrode oftransistor 29 is grounded, and a diode 30 and a capacitor 3l areconnected in parallel across the collector electrode of transistor 29and the ground. The diode 30 serves to ground a portion of the output ofthe collector output of transistor 29 for the purpose of lowering thereverse breakdown voltage thereof. A tank coil 32 is connected betweenthe collector electrode of transistor 29 and its positive source ofsupply to form a resonance circuit together with capacitor 31 to form afly-back pulse. Further, a series resonance circuit comprised by acapacitor 33 and an inductance coil 34 is connected between thecollector electrode of transistor 29 and the ground. This seriesresonance circuit has a resonance frequency equal to the resonancefrequency of the piezoelectric voltage transforming element. A drivesignal appearing at the juncture 35 between capacitor 33 and coil 34 ofthe series resonance circuit is impressed upon a drive electrode 2 ofthe piezoelectric voltage transforming element.

Although in this embodiment an output signal derived from the outputelectrode 4 of the piezoelectric voltage transforming element I is fedback to the oscillator through synchronizing circuit 16, as shown bydotted lines in FIG. 3, such a feedback signal may be taken from afeedback electrode 36 specially provided for the piezoelectric voltagetransforming ele ment 1.

I In this embodiment, a considerably high voltage is produced on theoutput side of the piezoelectric voltage transforming element. For thisreason, it is necessary to make sufficiently small the capacitance ofthe capacitor comprising the synchronizing circuit. Otherwise a voltagehigher than the insulating strength will be impressed upon transistor 17of oscillator 14 to damage the same. For this reason, in some cases itis advantageous to use a capacitor having a capacitance of the order ofseveral picofarad. In such a case, the stray capacitance of theapparatus may be used. More particularly, so long as the oscillationfrequency of the oscillator lies within a range capable of driving thepiezoelectric voltage transforming element 1, the first oscillation willdrive the piezoelectric voltage transforming element 1 and the outputvoltage thereof will be fed back to the base electrode of transistor 17of oscillator 14 thus locking the oscillation frequency of theoscillator to the resonance frequency of the piezoelectric voltagetransforming element.

Furthermore, while in the embodiment, the high voltage rectifyingcircuit 12 was shown as the type that can multiply the voltage by afactor of four it is to be understood that any other circuit that canmultiply the voltage by any factor may also be used.

As above described, this invention provides a novel self-exciting highvoltage generating apparatus utilizing a piezoelectric voltagetransforming element and provided with an efficient synchronizingcircuit that can lock the oscillation frequency of the oscillator to theresonance frequency of the piezoelectric voltage transforming element.

While l have shown and described in detail two forms of my invention byway of illustration, many modifications will undoubtedly occur to thoseskilled in the art. I therefore contemplate by the concluding portion ofthis specification to cover all such modifications as fall within thetrue spirit and scope of my invention.

What is claimed is:

l. A self-exciting type high voltage generating apparatus comprising apiezoelectric voltage transforming element provided with a driveelectrode and an output electrode, an oscillator having frequencydetermining elements establishing the oscillator frequency at afrequency corresponding to the resonant frequency of the piezoelectricelement, means for coupling the output from said oscillator to saiddrive electrode so that said piezoelectric element produces an outputvoltage at its output electrode which is substantially higher than thevoltage applied by said oscillator to its drive electrode, and acapacitive feedback circuit for feeding the output appearing at saidoutput electrode back to said oscillator whereby to lock the oscillationfrequency of said oscillator to the resonance frequency of saidpiezoelectric voltage transforming element, said feedback circuitcomprising a capacitor of small capacitance and high impedance relativeto the input im pedance of the point to which the feedback voltage isapplied to avoid damaging said point and minimize loading of saidelement.

2. The self-exciting type high voltage generator as claimed in claim 1wherein the oscillator and the piezoelectric element are arranged toform such capacitor by means of the stray capacitance existing betweensaid oscillator and said piezoelectric element.

3. The self-exciting type high voltage generator as claimed in claim 1wherein the output from saidpiezoelectric voltage transforming elementis stepped up and rectified.

4. The self-exciting type high voltage generator as claimed in claim 1wherein said oscillator comprises a blocking oscilla-- tor having atransistor connected therein to which the feedback from thepiezoelectric element is applied.

1. A self-exciting type high voltage generating apparatus comprising apiezoelectric voltage transforming element provided with a driveelectrode and an output electrode, an oscillator having frequencydetermining elements establishing the oscillator frequency at afrequency corresponding to the resonant frequency of the piezoelectricelement, means for coupling the output from said oscillator to saiddrive electrode so that said piezoelectric element produces an outputvoltage at its output electrode which is substantially higher than thevoltage applied by said oscillator to its drive electrode, and acapacitive feedback circuit for feeding the output appearing at saidoutput electrode back to said oscillator wheReby to lock the oscillationfrequency of said oscillator to the resonance frequency of saidpiezoelectric voltage transforming element, said feedback circuitcomprising a capacitor of small capacitance and high impedance relativeto the input impedance of the point to which the feedback voltage isapplied to avoid damaging said point and minimize loading of saidelement.
 2. The self-exciting type high voltage generator as claimed inclaim 1 wherein the oscillator and the piezoelectric element arearranged to form such capacitor by means of the stray capacitanceexisting between said oscillator and said piezoelectric element.
 3. Theself-exciting type high voltage generator as claimed in claim 1 whereinthe output from said piezoelectric voltage transforming element isstepped up and rectified.
 4. The self-exciting type high voltagegenerator as claimed in claim 1 wherein said oscillator comprises ablocking oscillator having a transistor connected therein to which thefeedback from the piezoelectric element is applied.